Piezo-electric/electrostrictive device and method of manufacturing same

ABSTRACT

The present invention provides a piezo-electric/electrostrictive device including a pair of thin plate sections in an opposed relation to each other, a fixing section for supporting the thin plate sections, and at least one pair of piezo-electric/electrostrictive elements are provided to the pair of thin plate sections. The thin plate sections include movable sections having end surfaces in an opposed relation. Recesses are formed between the thin plate sections and the fixing section and/or the movable sections.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/862,843, filed Jun. 7, 2004, which in turn is a continuation of U.S.application Ser. No. 10/211,872, filed Aug. 2, 2002, now U.S. Pat. No.6,772,492, which is a division of U.S. application Ser. No. 09/663,145,filed Sep. 15, 2000, now U.S. Pat. No. 6,455,981, which in turn is acontinuation-in-part of U.S. application Ser. No. 09/501,162, filed Feb.9, 2000, now abandoned, and U.S. application Ser. No. 09/524,042, filedMar. 13, 2000, now U.S. Pat. No. 6,498,419, and which claims the benefitof U.S. Provisional Application Ser. No. 60/218,191, filed Jul. 14,2000, the entireties of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a piezo-electric/electrostrictivedevice including movable sections which operate based on thedisplacement movement of a piezo-electric/electrostrictive element, apiezo-electric/electrostrictive device in which the displacement of themovable sections can be detected by a piezo-electric/electrostrictiveelement, and a method for producing the same. Specifically, the presentinvention relates to a piezo-electric/electrostrictive device havinghigh strength, high impact resistance, and high moisture resistance inwhich movable sections can be operated in a large movement efficiently,and a method for producing the same.

BACKGROUND OF THE INVENTION

Recently, in the field of optics, magnetic recording, and precisionprocessing, there is a demand for a displacement element capable ofadjusting the length and position of an optical path by orders ofsubmicron. In an attempt to satisfy such a demand, developments havebeen pursued for a displacement element which utilizes a displacementgenerated by an inverse piezo-electric effect and an electrostrictiveeffect obtained when a voltage is applied to apiezo-electric/electrostrictive material (for example, ferroelectricsubstances and the like).

As a conventional displacement element such as described above, JapaneseUnexamined Patent Publication No. 10-136665 discloses a piezo-electricactuator having a structure where a piezo-electric/electrostrictivematerial is formed into a plate-like body which is then perforated,thereby integrally forming a fixing section, movable sections, and abeam section for supporting them into one-piece unit, and an electrodelayer is formed in the beam section. In thispiezo-electric/electrostrictive actuator, when a voltage is applied tothe electrode layer, the beam section shrinks in a direction thatconnects the fixing section to the movable sections due to the inversepiezo-electric effect and electrostrictive effect. As a result, themovable sections can be displaced along an arc or rotatively displacedwithin the surface of the plate-like body.

Japanese Unexamined Patent Publication No. 63-64640 discloses atechnique using an actuator with a bimorph. The electrode of the bimorphis divided into a plurality of electrodes, and the divided electrodesare selectively driven. In this manner, positioning can be performedwith high accuracy at high speed. This prior art publication shows (inparticular, in FIG. 4) the structure where two bimorphs are positionedin an opposed relation to each other.

However, the conventional actuators described above are entirelyconstituted by fragile materials which are relatively heavy in weight.Therefore, they have low mechanical strength, and are poor in handlingcharacteristics and impact resistance.

Conventionally, in an attempt to improve the mechanical strength of theconventional actuators, the strength of the section easy to vibrate hasbeen enhanced. For this purpose, the enhancement in the rigidity of thevibration section has been conducted. The enhancement adversely affectsthe basic properties of the actuator itself, such as resonancecharacteristics and displacement, and causes a problem in that theadjustment of the basic properties becomes difficult.

SUMMARY OF THE INVENTION

The present invention has been made in order to improve the impactresistance of the force sensor described in Japanese Patent ApplicationsNos. 11-114669, 11-259006, and 11-259007 which are prior applicationsfiled by the present inventors. Furthermore, the present invention hasbeen made based on the finding that, in the force sensor described inthe U.S. patent application Ser. No. 09/501,162 which utilized apiezo-electric body, the impact exerted to the operating body from theoutside is easily adsorbed by a viscoelastic body provided into a narrowslot formed under the supporting bed, thereby improving the impactresistance of the vibration plate.

In order to enhance the impact resistance of the device, while givingonly a small influence on the basic properties of the device itself,according to the present invention, a piezo-electric/electrostrictivedevice includes a pair of thin plate sections in an opposed relation toeach other, a fixing section for supporting the thin plate sections, thepair of thin plate sections having a movable section at a top endthereof, and at least one of the pair of thin plate sections having oneor more piezo-electric/electrostrictive elements, wherein a filler isprovided in recesses between the thin plate sections and the movablesections, or in recesses between the thin plate sections and the fixingsection. With this arrangement, even if the thin plate sections producelarge displacements by receiving a large impact from the outside, thestress generated at the boundary between the thin plate sections and themovable sections or between the thin plate sections and the fixingsection is dispersed into the filler provided in the recess. In thismanner, there is no damage of the device which has been conventionallyresulted from the concentration of the stress, and the impact resistanceof the thin plate sections is enhanced.

In the present invention, the concept of thepiezo-electric/electrostrictive device resides in that electrical energyand mechanical energy are alternately converted by apiezo-electric/electrostrictive element included therein. Therefore, thepiezo-electric/electrostrictive device is most preferably used as anactive device, such as various actuators and vibrators, and especially adisplacement device which utilizes a displacement created by a backwardvoltage effect and electrostrictive effect. In addition, thepiezo-electric/electrostrictive device is also preferable as a passivedevice such as acceleration sensor elements and impact sensor elements.

As a material for the filler, an organic resin, such as an adhesive,glass, a mixture of an organic resin and ceramics, metal, or a mixtureof metal and ceramics may be used. The filler may be porous or dense. Itis preferable that the filler is highly porous as its hardnessincreases, and is highly dense as its flexibility increases. The fillerlayer is preferably adhered to the thin plate section, and the movablesection, the fixing section, and the filler layer itself have elasticityor flexibility. Furthermore, the filler itself is preferably aviscoelastic body, because a filler with viscoelasticity effectivelyadsorbs the impact from the outside.

The recess into which the filler is provided has a shape of rectangle.Alternatively, the surface of the recess formed by the inner surface ofthe movable section or fixing section in an opposed relation to the thinplate section may be in a step-like or tapered shape. When the device isproduced by laminating green sheets, the recess may be formed by asingle layer or multiple layers. When the recess is formed by a singlelayer, the preferable thickness of the recess is 0.01 to 0.3 mm, and thepreferable depth thereof is 0.03 to 1 mm. The preferable ratio ofthickness to depth (thickness/depth) is 0.01 to 10, and more preferably0.1 to 3. When the recess is formed by multiple layers, the thickness ofthe recess is preferably increased in the longitudinal direction of thethin plate section.

The thickness of the recess indicates the length of the shortest portionin the recess. The recess does not necessarily have a uniform size, butits opening or bottom may have a larger size.

Preferably, a method for producing a piezo-electric/electrostrictivedevice including a pair of thin plate sections in an opposed relation toeach other, a fixing section for supporting the thin plate sections, thepair of thin plate sections having a movable section at a top endthereof, and at least one of the pair of thin plate sections having oneor more piezo-electric/electrostrictive elements, includes the steps offorming and preparing a first ceramic green sheet to be the thin platesection, a second ceramic green sheet having a first window section, anda third ceramic green sheet having a window section smaller than thefirst window section, and interposing at least the second ceramic greensheet between the first and third ceramic green sheets to prepare alaminated body of a plurality of ceramic green sheets.

It is also preferable that a method for producing apiezo-electric/electrostrictive device including a pair of thin platesections in an opposed relation to each other, a fixing section forsupporting the thin plate sections, the pair of thin plate sectionshaving a movable section at a top end thereof, and at least one of thepair of thin plate sections having one or morepiezo-electric/electrostrictive elements, includes the steps of formingand preparing a first ceramic green sheet to be the thin plate section,and a second ceramic green sheet having a window section, andinterposing a sheet containing a high-melting point metal between thefirst ceramic green sheet and the second ceramic green sheet.

In addition, it is preferable that the sheet containing the high-meltingpoint metal is formed by a printing method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a piezo-electric/electrostrictivedevice.

FIG. 2 is an explanatory diagram showing the movement of apiezo-electric/electrostrictive device.

FIG. 3 is an explanatory diagram showing another shape of filler filledinto the recess.

FIG. 4 is a perspective view showing a piezo-electric/electrostrictivedevice having a recess of another type.

FIG. 5 is an explanatory diagram showing a filler having a shapedifferent from the shape shown in FIG. 4.

FIG. 6 is a perspective diagram showing apiezo-electric/electrostrictive device having a recess of another type.

FIG. 7 is an explanatory diagram showing a filler having a shapedifferent from the shape shown in FIG. 6.

FIG. 8 is a perspective view showing a piezo-electric/electrostrictivedevice having a recess of another type.

FIG. 9 is an explanatory diagram showing green sheets to be laminated ontop of each other.

FIG. 10 is an explanatory diagram showing the state where the greensheets are laminated on top of each other.

FIG. 11 is an explanatory diagram showing the state after thepiezo-electric layer is formed.

FIG. 12 is an explanatory diagram showingpiezo-electric/electrostrictive device after cutting.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments in which the piezo-electric/electrostrictivedevice of the present invention is obtained will be described in detail.

FIG. 1 is a perspective view showing a piezo-electric/electrostrictivedevice 10. The piezo-electric/electrostrictive device 10 has a substrate16 in which a pair of thin plate sections 12 a and 12 b in an opposedrelation to each other, and a fixing section 14 for holding the thinplate sections 12 a and 12 b are integrally formed. A part of the pairof thin plate sections 12 a and 12 b is respectively formed withpiezo-electric/electrostrictive elements 18 a and 18 b.

In the piezo-electric/electrostrictive device 10, the pair of thin platesections 12 a and 12 b are displaced by driving thepiezo-electric/electrostrictive elements 18 a and/or 18 b, or thedisplacement of the pair of thin plate sections 12 a and 12 b isdetected by the piezo-electric/electrostrictive elements 18 a and/or 18b.

The top end of the respective thin plate sections 12 a and 12 b projectsinwardly to be thick. The thick portions serve as movable sections 20 aand 20 b which are displaced in accordance with the displacementmovement of the thin plate sections 12 a and 12 b. Hereinafter, the topends of the thin plate sections 12 a and 12 b are referred to as movablesections 20 a and 20 b.

At the boundaries between the top ends of the thin plates 12 a and 12 b,and the movable sections 20 a and 20 b, respectively, recesses 20 c and20 d are formed along a longitudinal direction of the thin platesections 12 a and 12 b. In the respective recesses 20 c and 20 d, afiller is provided. Similarly, at the boundaries between the bottom endsof the thin plates 12 a and 12 b and the fixing section 14, recesses 14a and 14 b are formed along a longitudinal direction of the thin platesections 12 a and 12 b, respectively. In the recesses 14 a and 14 b, afiller is provided.

The substrate 16 may have a single structure made of ceramics alone, oralternatively, may have a hybrid structure made of ceramics and ametallic material in combination.

The substrate 16 also may have a structure in which the members thereofare attached to each other by an adhesive such as an organic resin andglass, a ceramic-integrated structure in which ceramic green sheets arelaminated on top of each other and are sintered into one-piece unit, ora metal-integrated structure in which metallic members are integratedinto one-piece unit by brazing, soldering, eutecting bonding, orwelding. Preferably, the substrate 16 is formed with a ceramic laminatedbody produced by sintering ceramic green laminated body into a one-pieceunit.

When the substrate has a ceramic-integrated structure, no adhesive isused at the connections between its members. Without the use ofadhesive, the substrate undergoes almost no change of state with theelapse of time, and therefore, this structure is advantageous in thathigh reliability is attained at the connections between the members, andhigh rigidity is also attained. In addition, this structure can beeasily produced by a ceramic green sheet laminating method which will bedescribed later.

The piezo-electric/electrostrictive elements 18 a and 18 b are preparedindependently from the substrate 16, as will be described later, andthen are attached to the substrate 16 with an adhesive such as anorganic resin and glass, or by a method such as brazing, soldering,eutectic bonding and the like. Alternatively, thepiezo-electric/electrostrictive elements 18 a and 18 b are directly andintegrally formed into the substrate 16 by a film forming method,instead of being attached to the substrate 16.

The piezo-electric/electrostrictive elements 18 a and 18 b respectivelyinclude a piezo-electric/electrostrictive layer 22, and a pair ofelectrodes 24 and 26 formed on both sides of thepiezo-electric/electrostrictive layer 22. Among the pair of electrodes24 and 26, at least the electrodes 24 are formed on the pair of thinplate sections 12 a and 12 b.

In one embodiment of the present invention, a description is mainly madeto the case where the piezo-electric/electrostrictive elements 18 a and18 b have the following structure. That is, thepiezo-electric/electrostrictive layer 22, and the pair of electrodes 24and 26 respectively have a multilayered structure. The electrodes 24 andthe electrodes 26 are alternately laminated to each other in such amanner that the cross-section of the laminated electrodes 24 and 26 issubstantially in the form of comb. The portion where the electrodes 24and the electrodes 26 overlap each other in a state of interposing thepiezo-electric/electrostrictive layer 22 therebetween has a multistagestructure. However, the structure of the piezo-electric/electrostrictivelayer 22 and the pair of electrodes 24 and 26 is not limited to themultilayered structure, but may be a single-layered structure. Thenumber of the layers is not specifically limited, however, ten layers orsmaller is preferable, and five layers or smaller is more preferable. Inaddition, only one of the piezo-electric/electrostrictive layers 18 a or18 b may be formed. The number of the layers of thepiezo-electric/electrostrictive layer 22, and the electrodes 24 and 26may be different from each other.

FIG. 1 shows the case where the piezo-electric/electrostrictive layer 22has a three-layered structure. The electrodes 24 is formed into a shapeof comb so as to be positioned under the lower surface of the firstlayer of the piezo-electric/electrostrictive layer 22 (i.e., on the sidesurface of the thin plate sections 12 a and 12 b) and on the uppersurface of the second layer thereof. The other electrodes 26 are formedinto the shape of a comb so as to be positioned on the upper surface ofthe first layer of the piezo-electric/electrostrictive layer 22, and onthe upper surface of the third layer thereof. In this structure, sincethe electrodes 24 and the other electrodes 26 are respectively connectedto each other into common electrodes, the number of the terminals 28 and30 can be decreased. In this manner, upsizing of thepiezo-electric/electrostatic elements 18 a and 18 b can be suppressedeven though they are formed in a multilayered structure.

The application of voltage to the pair of electrodes 24 and 26 isconducted through the terminals (i.e. pads) 28 and 30 which are formedon the electrodes 24 and 26 located at the position above the sidesurfaces of the fixing section 14 (i.e. surfaces on which thepiezo-electric/electrostrictive elements are formed). The terminals 28and 30 are formed so that the terminal 28 corresponding to theelectrodes 24 is located at a position close to the bottom end of thefixing setion 14, and the terminal 30 at the outer space sidecorresponding to the electrodes 26 is located at the position close tothe inner wall of the fixing section 14.

In this case, the fixation of the piezo-electric/electrostrictive device10 can be conducted using its surfaces other than the surfaces on whichthe terminals 28 and 30 are formed. As a result, high reliability can beattained for both the fixation of the piezo-electric/electrostrictivedevice 10, and the electric connection between the circuits and theterminals 28 and 30. In this structure, the terminals 28 and 30 areelectrically connected to the circuits by a flexible printing circuit(also referred to as FPC), flexible flat cable (also referred to asFFC), wire bonding and the like.

By use of the piezo-electric/electrostrictive elements 18 a and 18 bhaving a multilayered structure, the driving force of the actuators 19 aand 19 b is increased, and large displacement is attained accordingly.In addition, the rigidity of the piezo-electric/electrostrictive device10 itself is also increased, and high resonance frequency is attainedaccordingly thereby easily speeding-up the displacement movement.

As the actuators 19 a and 19 b have an increased number of stages, theirdriving force increases; however, consumption of the electric power alsoincreases accordingly. Therefore, when the present invention is carriedout, the number of stages of the actuators 19 a and 19 b and the likemay be determined in accordance with the application and use conditionsof the piezo-electric/electrostrictive device. In thepiezo-electric/electrostrictive device 10 according to this embodiment,by use of the piezo-electric/electrostrictive elements 18 a and 18 b,the width (i.e. the distance in the direction of Y axis) of the thinplate sections 12 a and 12 b basically remains unchanged even if thedriving force of the actuators 19 a and 19 b are increased. Athus-structured piezo-electric/electrostrictive device 10 is morepreferable for use in an actuator for positioning a magnetic head for ahard disk and ringing control, which is used in a space with anextremely small width.

Next, the movement of the piezo-electric/electrostrictive device 10 willbe described referring to FIG. 2.

When the two piezo-electric/electrostrictive elements 18 a and 18 b arein a natural state, that is, the piezo-electric/electrostrictiveelements 18 a and 18 b do not perform a displacement movement, thelongitudinal axis m of the piezo-electric/electrostrictive device 10substantially coincides with the central axis of the fixing section 14.

In this state, a sine wave Wa having a specified bias electric potentialVb is applied to the pair of electrodes 24 and 26 of thepiezo-electric/electrostrictive elements 18 a. On the other hand, a sinewave Wb having a phase different from the sine wave Wa by substantially180° is applied to the pair of electrodes 24 and 26 of the otherpiezo-electric/electrostrictive element 18 b.

At a stage where, for example, a voltage of a maximum value is appliedto the pair of electrodes 24 and 26 of thepiezo-electric/electrostrictive element 18 a, thepiezo-electric/electrostrictive layer 22 of thepiezo-electric/electrostrictive layer 22 displaces to shrink in adirection toward its major surface. As shown in FIG. 2, a stress isapplied to the thin plate section 12 a in such a direction as to causethe thin plate section 12 a to become warped toward, for example, aright direction as shown by an arrow A, and as a result, the thin platesection 12 a is warped toward a right direction. At this time, since novoltage is applied to the pair of electrodes 24 and 26 of the otherpiezo-electric/electrostrictive element 18 b, the thin plate section 12b follows the warpage of the thin plate section 12 a and is also warpedtoward a right direction. As a result, the movable sections 20 a and 20b, and the spacer 37 displace toward, for example, a right directionwith respect to the longitudinal axis m of thepiezo-electric/electrostrictive device 10 b. The amount of displacementvaries in accordance with the maximum value of the voltage applied tothe piezo-electric/electrostrictive elements 18 a and 18 b. For example,as the maximum value of the voltage increases, the amount ofdisplacement becomes larger.

In the case where a piezo-electric/electrostrictive material having highcoercive electric field is employed as a material of thepiezo-electric/electrostrictive layer 22, the bias electric potentialmay be adjusted so that the minimum values of the sine waves Wa and Wbare at slightly negative levels. In this case, either one of thepiezo-electric/electrostrictive elements to which the sine wave Wa or Wbat a slightly negative level is applied (for example, thepiezo-electric/electrostrictive element 18 b) is driven, and a stress inthe same direction as the direction of warpage of the thin plate section12 a is applied to the thin plate section 12 b. As a result, it becomespossible to further increase the amount of displacement of the movablesections 20 a and 20 b, and the spacer 37. That is, the employment ofthe waveform described above makes it possible that thepiezo-electric/electrostrictive elements 18 b or 18 a to which the sinewave at a negative level is applied supports the function of thepiezo-electric/electrostrictive elements 18 a or 18 b which plays a mainrole of the displacement movement.

As described above, in the piezo-electric/electrostrictive device 10according to one embodiment of the present invention, a smalldisplacement of the piezo-electric/electrostrictive elements 18 a and 18b is amplified into a large displacement movement by using the warpageof the thin plate sections 12 a and 12 b, and then is transmitted to themovable sections 20 a and 20 b. In this manner, the movable sections 20a and 20 b can be largely displaced with respect to the longitudinalaxis m of the piezo-electric/electrostrictive device 10 b.

Particularly, in this embodiment, the movable sections 20 a and 20 b areformed with attachment surfaces 34 a and 34 b in an opposed relation toeach other. The distance Lc between the attachment surfaces 34 a and 34b is set at a value of about 1.5 times longer than the length Df of themovable sections 20 a and 20 b. In addition, a large spacer 37 isattached between the attachment surfaces 34 a and 34 b via an adhesive38. In this case, the attachment surfaces 34 a and 34 b in an opposedrelation to each other are spaced from each other, or a spacer 37 havinga weight smaller than the constituent elements of the movable sections20 a and 20 b is interposed between the attachment surfaces 34 a and 34b in an opposed relation to each other. In this manner, weight reductionof the movable sections 20 a and 20 b can be effectively achieved, andthe resonance frequency can be increased without lowering thedisplacement amount of the movable sections 20 a and 20 b.

In this embodiment, the term “frequency” means a frequency of thewaveform of voltage obtained when the voltage applied to the pair ofelectrodes 24 and 26 is alternately switched, and the movable sections20 a and 20 b are displaced in left and right directions. The term“resonance frequency” means a maximum frequency at which the movablesections 20 a and 20 b can manage to displace in a specified vibrationmode.

In the piezo-electric/electrostrictive device 10 according to theembodiment of the present invention, the movable sections 20 a and 20 b,the thin plate sections 12 a and 12 b, and the fixing section 14 areintegrally formed into one-piece unit. All of them are not required tobe made of a piezo-electric/electrostrictive material, which is amaterial relatively heavy in weight. The piezo-electric/electrostrictivedevice with this structure 10 has high mechanical strength, excellenthandling characteristics, high impact resistance and moistureresistance, and is resistant to harmful vibrations (for example,residual vibrations in high-speed operation or vibrations generated by anoise).

Furthermore, in this embodiment of the present invention, in the casewhere the attachment surfaces 34 a and 34 b in an opposed relation toeach other are spaced, the movable section 20 a including the attachmentsurface 34 a and the movable section 20 b including the attachmentsurface 34 b can be easily warped, and become resistant to deformation.This structure gives excellent handling characteristics to thepiezo-electric/electrostrictive device 10.

Due to the presence of the attachment surfaces 34 a and 34 b in anopposed relation, the movable sections 20 a and 20 b respectively have alarge surface area. When another member is attached to the movablesections 20 a and 20 b, large area can be used for attaching the member,thereby firmly attaching the member. When taking into consideration thecase where a member is attached with an adhesive for example, the memberis attached through not only the major surfaces of the movable sections20 a and 20 b but also the attachment surface 34 a and 34 b in anopposed relation. In this manner, the member can be firmly attached.

In this embodiment of the present invention, thepiezo-electric/electrostrictive elements 18 a and 18 b are formed withthe piezo-electric/electrostrictive layer 22, and the pair of electrodes24 and 26 which interposes the piezo-electric/electrostrictive layer 22therebetween. Among the pair of electrodes 24 and 26, the electrode 24is directly formed at least on the side surface of the thin platesections 12 a and 12 b. In this manner, the vibration generated by thepiezo-electric/electrostrictive elements 18 a and 18 b can beefficiently transmitted to the movable sections 20 a and 20 b throughthe thin plate sections 12 a and 12 b. As a result, responseness isenhanced.

In this embodiment of the present invention, as shown in FIG. 1 forexample, the portion in which the pair of electrodes 24 and 26 overlapeach other in the state of interposing thepiezo-electric/electrostrictive layer 22 therebetween (i.e., asubstantial driving portion 40) is continuously formed starting from apart of the fixing section 14 to a part of the thin plate sections 12 aand 12 b. If the substantial driving portion 40 is so constructed as toextend to reach a part of the movable sections 20 a and 20 b, there maybe the possibility that the displacement movement of the movablesections 20 a and 20 b counteracts the deformation of the substantialdriving portion 40 and the deformation of the thin plate sections 12 aand 12 b, and large displacement cannot be attained. Contrarily, in thisembodiment, the substantial driving portion 40 is so constructed as notto extend to reach the movable sections 20 a and 20 b, but to cover onlythe fixing section 14. This structure avoids the disadvantage that thedisplacement movement of the movable sections 20 a and 20 b is limited,thereby increasing the displacement amount of the movable sections 20 aand 20 b.

On the contrary, when the piezo-electric/electrostrictive elements 18 aand 18 b are formed on a part of the movable sections 20 a and 20 b, itis preferable that the substantial driving portion 40 is positioned inan area extending from a part of the movable sections 20 a and 20 b to apart of the thin plate sections 12 a and 12 b. This is because if thesubstantial driving portion 40 is so constructed as to extend to reach apart of the fixing section 14, the displacement movement of the movablesections 20 a and 20 b is restricted, as described above.

In the above-described embodiment, the movable sections 20 a and 20 bhave attachment surfaces 34 a and 34 b respectively, and the spacer 37is attachedly mounted therebetween. Alternatively, it is possible toform end surfaces 34 a and 34 b in the fixing section 14. In this case,for example, the movable sections 20 a and 20 b are integrally combinedinto one-piece unit at the top end of the pair of thin plate sections 12a and 12 b, while the end surfaces 34 a and 34 b in an opposed relationto each other are formed in the fixing section 14.

In this arrangement, the piezo-electric/electrostrictive device 10 c canbe firmly fixed to a specified fixing position, and increasedreliability can be obtained, on top of the advantages obtained in thecase where the movable sections 20 a and 20 b respectively have theattachment surfaces 34 a and 34 b in an opposed relation to each other.The length of the substantial driving portion 40 is preferably 20 to 95percent, and more preferably 40 to 80 percent with respect to the lengthof the thin plate section 12 a and 12 b.

When the recess has a rectangular shape, the filler to be providedtherein may have shapes as shown in FIG. 3. In the embodiment shown inFIG. 1, the filler can be filled up to the opening of the recess havinga rectangular shape. In the embodiment shown in FIG. 3(a), the filler isfilled about halfway the recess, and the area near the opening is freefrom the filler. In this case, the filler in a specified amount isfilled into the recess. The arrangement shown in FIG. 3(a) has anadvantage that the end surface of the fillers can be made into the sameshape each other. If the recess has a hollow portion in which no filleris provided is formed at its bottom, the effect of dispersing the stressis not adversely affected.

In the embodiment shown in FIG. 3(b), the filler is provided in therecess beyond the opening thereof. This arrangement is advantageous inthe case where the filler has weak adhesion, because the filler can beattached inside the recess in a large area, thereby increasing theadhesion of the entire filler. By forming the outer surface of thefiller into an R-shape, the filler can be more firmly fixed into therecess, and never peels off at its end portion.

Alternatively, the filler formed into the shape as shown in FIG. 3(c)may be provided in the recess. In this case, the shape of the areabetween the thin plate section and the fixing section or the movablesection assumes a step-like shape, that is, the area is occupied by thecorner of the filler. This shape of filler is effective, together withthe physical properties of the filler, in further reducing theconcentration of stress onto the base portion of the thin platesections.

Next, a preferable example of the structure of thepiezo-electric/electrostrictive device 10 according to an embodiment ofthe present invention will be described.

In order to assure the displacement movement of the movable sections 20a and 20 b, the distance Dg of the substantial driving portion 40 of thepiezo-electric/electrostrictive elements 18 a and 18 b which overlapsthe movable sections 20 a and 20 b is preferably made to be ½ or largerthe thickness Dd of the thin plate sections 12 a and 12 b.

Defining the distance between the inner walls of the thin plate sections12 a and 12 b as Da (i.e., the distance in the direction of X axis), andthe width of the thin plate sections 12 a and 12 b as Db (i.e. thedistance in the direction of Y axis), the ratio of Da to Db (Da/Db) iswithin a range of 0.5 to 20, preferably 1 to 15, and more preferably 1to 10. The ratio Da/Db is a value determined based on the finding that,at this value, a large amount of displacement of the movable sections 20a and 20 b can be obtained, and the displacement within X-Z plane can bepredominantly obtained.

Defining the length between the thin plate sections 12 a and 12 b (i.e.,the distance in the direction of Z axis) as De, and the distance betweenthe inner walls of the thin plate sections 12 a and 12 b as Da, theratio of De to Da (De/Da) is preferably made to 0.5 to 10, and morepreferably 0.5 to 5. The ratio De/Da is a value determined based on thefinding that, at this value, a large amount of displacement of themovable sections 20 a and 20 b interposing the spacer 37 therebetweencan be obtained, and the displacement movement can be conducted at highresonance frequency (i.e., high response speed can be attained).

According to the present invention, in order that thepiezo-electric/electrostrictive device 10 has a structure in which theagitated displacement or vibration in the direction of the Y-axis issuppressed, and a high responsiveness is achieved as well as a largedisplacement at relatively low voltages, the ratio of Da/Db ispreferably made to 0.5 to 20, and the ratio of De/Da is preferably 0.5to 10. More preferably, the ratio of Da/Db is 1 to 10, and the ratio ofDe/Da is 0.5 to 5.

Furthermore, in the piezo-electric/electrostrictive device 10, a holesection 42 is formed by the inner walls of the pair of thin plates 12and 12 b, the inner walls of the movable section 20 a and 20 b, and theinner wall of the spacer 37 (and the inner wall of the adhesive 38), andthe inner wall of the fixing section 14. The hole section 42 ispreferably filled with a gel material such as silicon gel. In aconventional case, the displacement movement of the movable sections 20a and 20 b is usually restricted by the presence of the filler.Contrarily, in the embodiment of the present invention, the weight ofthe movable sections 20 a and 20 b is reduced by forming the endsurfaces 34 a and 34 b on the movable sections 20 a and 20 b, and anincrease in the amount of the displacement of the movable sections 20 aand 20 b is aimed. As a result, there is no restriction by the filler onthe displacement movement of the movable sections 20 a and 20 b, and ahigh resonance frequency and high rigidity are advantageously attainedas an effect of the presence of the filler.

The length Df of the movable sections 20 a and 20 b (i.e., the distancein the direction of Z axis) as Df is preferably short. By using themovable sections 20 a and 20 b short in length, the weight of the devicecan be reduced, and the resonance frequency can be increased. Inaddition, the displacement can be enhanced when an article is held.However, in order to give high rigidity in the direction of X axis tothe thin plate sections 12 a and 12 b, and to ensure their properdisplacement, the ratio of the length Df of the movable sections 20 aand 20 b with respect to their thickness Dd is made to be 2 or larger,and preferably 5 or larger.

The actual size of each member is decided taking into consideration theattachment area between the movable sections 20 a and 20 b and anothermember attached thereto, the attachment area between the fixing section14 and another member attached thereto, the attachment area between theterminals for electrodes and the device, the strength, durability, andrequired amount of displacement, resonance frequency of the entirepiezo-electric/electrostrictive device 10, the driving voltage, and thelike.

Specifically, the distance Da between the inner walls of the thin platesections 12 a and 12 b is preferably 100 to 2000 μm, and more preferably200 to 1600 μm. The width Db of the thin plate sections 12 a and 12 b ispreferably 50 to 2000 μm, and more preferably 100 to 500 μm. Thethickness Dd of the thin plate sections 12 a and 12 b is made to besmaller than the width Db of the thin plate sections 12 a and 12 b, thatis, to satisfy the relationship of Db>Dd in order that the agitateddisplacement, which is a displacement component in the direction of Yaxis, can be effectively suppressed, and is preferably made to 2 to 100μm, and more preferably 10 to 80 μm.

The length De of the thin plate sections 12 a and 12 b is preferablymade to 200 to 3000 μm, and more preferably 300 to 2000 μm. The lengthDf of the movable sections 20 a and 20 b is preferably made to 50 to2000 μm, and more preferably 100 to 1000 μm, and much more preferably200 to 600 μm.

By employing the structure described above, the displacement in thedirection of Y-axis never exceeds 10 percent with respect to thedisplacement in the direction of X-axis, while the drive at a lowvoltage is possible and the displacement component in the direction ofY-axis can be suppressed to 5 percent or lower by properly adjusting thesize of each member so that the actual sizes satisfies the size ratiosdescribed above. Specifically, the movable sections 20 a and 20 b aredisplaced in the direction of substantially one axis, that is, X-axis.In addition, high responsiveness is attained, and large displacement canbe obtained at relatively low voltages.

In the piezo-electric/electrostrictive device 10, the movable sections20 a and 20 b, and the fixing section 14 assume a rectangular shape,unlike the plate-like shape as of a conventional device (where thethickness in the direction perpendicular to the displacement directionis small). In addition, the thin plate sections 12 a and 12 b areprovided in such a manner that the movable sections 20 a and 20 b aresuccessive with the side surface of the fixing section 14. As a result,the rigidity of the piezo-electric/electrostrictive device 10 in thedirection of Y axis can be selectively increased.

Specifically, in the piezo-electric/electrostrictive device 10 having asize constitution as described above, the movable sections 20 a and 20 balone can be selectively moved within a plane (i.e., within a XZ plane),while suppressing the movement of the movable sections 20 a and 20 b ina YZ plane (that is, the movement in the agitated direction).

Next, each constituent element of the piezo-electric/electrostrictivedevice 10 according to an embodiment of the present invention will bedescribed.

As described above, the movable sections 20 a and 20 b move based on thedriving amount of the thin plate sections 12 a and 12 b, and havevarious members in accordance of the intended use of thepiezo-electric/electrostrictive device 10. For example, when thepiezo-electric/electrostrictive device 10 is used as a displacementelement, a screening plate for shutting out light is mounted.Particularly, when the piezo-electric/electrostrictive device 10 is usedfor positioning a magnetic head of hard disk drive or a ringingsuppressing mechanism, a member is required for positioning, such as amagnetic head, a slider having a magnetic head, a suspension having aslider and the like is mounted thereon.

As described above, the fixing section 14 supports the thin platesections 12 a and 12 b, and the movable sections 20 a and 20 b. When thepiezo-electric/electrostrictive device 10 is used for positioning themagnetic head of the hard disk drive, the entirepiezo-electric/electrostrictive device 10 is firmly fixed by supportedlyfixing the fixing section 14 to a carriage arm attached to a voice coilmotor (VCM), a fixing plate or a suspension attached to the carriagearm. In some cases, to the fixing section 14, terminals 28 and 30 orother members for driving the piezo-electric/electrostrictive elements18 a and 18 b may be provided.

As a material for constituting the movable sections 20 a and 20 b, andthe fixing section 14, any material may be employed as far as it hassufficient rigidity. Ceramics, which enable the employment of a ceramicgreen sheet laminating method, are preferred. Examples of the materialinclude materials containing zirconia, such as stabilized zirconia andpartially stabilized zirconia, alumina, magnesia, silicon nitride,aluminum nitride, titanium oxide, or a mixture thereof as a maincomponent. Among them, a material containing zirconia, and especially amaterial containing stabilized zirconia and a material containing apartially stabilized zirconia a main component are preferable, becausethey exhibit high mechanical strength and high toughness.

As described above, the thin plate sections 12 a and 12 b are driven bythe displacement of the piezo-electric/electrostrictive elements 18 aand 18 b. The thin plate sections 12 a and 12 b are members in the formof a flexible thin plate. The thin plate sections 12 a and 12 b amplifythe shrinking displacement of the piezo-electric/electrostrictiveelements 18 a and 18 b provided on the surface thereof into a flexiondisplacement, and transmit the flexion displacement into the movablesections 20 a and 20 b. The shape and material of the thin platesections 12 a and 12 b are not specifically limited as long as they havesufficient flexibility and mechanical strength to the extent that theyare not damaged by the flexion deformity, and are properly determinedtaking into consideration the responsiveness and operability of themovable sections 20 a and 20 b.

The thickness Dd of the thin plate sections 12 a and 12 b is preferably2 to 100 μm, and the thickness of the thin plate sections 12 a and 12 b,and the piezo-electric/electrostrictive elements 18 a and 18 b incombination, is preferably 7 to 500 μm. The thickness of the electrodes24 and 26 is preferably 0.1 to 50 μm, and the thickness of thepiezo-electric/electrostrictive layer 22 is preferably 3 to 300 μm.

As a material for constituting the thin plate sections 12 a and 12 b,the same kinds of ceramics as those used for the movable sections 20 aand 20 b and the fixing section 14 are preferably used. Among them, themost preferable is a material containing stabilized zirconia as a maincomponent and a material containing a partially stabilized zirconia,because they exhibit high mechanical strength and high toughness even ifthey are made into a thin plate, and have a small reactiveness with thematerials of the piezo-electric/electrostrictive layer and electrodes.

The zirconia is preferably stabilized or partially stabilized in thefollowing manner. That is, compounds for stabilizing or partiallystabilizing the zirconia include yttrium oxide, ytterbium oxide, ceriumoxide, calcium oxide, and magnesium oxide. At least one is added to thezirconia, or two or more of them in combination is added to thezirconia, thereby obtaining the aimed stabilized or partially stabilizedzirconia.

The addition amount of the respective compound is, in the case ofyttrium oxide and ytterbium oxide, 1 to 30 mole percent, and preferably1.5 to 10 mole percent. In the case of cerium oxide, 6 to 50 molepercent, and preferably 8 to 20 mole percent. In the case of calciumoxide and magnesium oxide, 5 to 40 mole percent, and preferably 5 to 20mole percent. Among them, it is preferable to use yttrium oxide as astabilizer. In this case, the addition amount of the yttrium oxide is1.5 to 10 mole percent, and more preferably 2 to 4 mole percent. It isalso possible to add additives, such as a sintering assistant, such asalumina, silica, and transition metal oxides in an amount ranging from0.05 to 20 weight percent. When the piezo-electric/electrostrictiveelements 18 a and 18 b are formed by a film formation method where greensheets are sintered to be integrated into one-piece unit, it is alsopreferable to add additives such as alumina, magnesia, and transitionmetal oxides.

In order to obtain high mechanical strength and a stabilized crystalphase, the average particle diameter of the zirconia crystals ispreferably 0.05 to 3 μm, and more preferably 0.05 to 1 μm. In addition,as described above, the thin plate sections 12 a and 12 b may beconstituted by the same type of ceramics as that used for the movablesections 20 a and 20 b and the fixing section 14. Preferably, it isadvantageous to use the same material for all the thin plate sections 12a and 12 b, the movable sections 20 a and 20 b, and the fixing section14, in order to attain high reliability at the connection areastherebetween, to give high strength to thepiezo-electric/electrostrictive device 10, and to prevent complicatedproduction of the device.

The piezo-electric/electrostrictive elements 18 a and 18 b at least havethe piezo-electric/electrostrictive layer 22, and the pair of electrodes24 and 26 for applying an electric field to thepiezo-electric/electrostrictive layer 22. As thepiezo-electric/electrostrictive elements 18 a and 18 b, apiezo-electric/electrostrictive element of a unimorph-type, abimorph-type or the like may be used. Among them, the unimorph-typeelement is more suitable for use in the piezo-electric/electrostrictivedevice 10, because in combination with the thin plate sections 12 a and12 b, the unimorph-type element has a higher ability to stabilize theamount of displacement generated and is advantageous in reducing theweight of the device.

It is preferable that, as shown in FIG. 1, thepiezo-electric/electrostrictive elements 18 a and 18 b are formed at theside surface of the thin plate sections 12 a and 12 b. This structure ispreferable in that the thin plate sections 12 a and 12 b can producelarger displacement movement.

As a material for the piezo-electric/electrostrictive layer 22,piezo-electric ceramics are preferably used. Alternatively, it is alsopossible to use electrostrictive ceramics, ferroelectric ceramics, orantiferroelectric ceramics. When the piezo-electric/electrostrictivedevice 10 is used for positioning a magnetic head of hard disk drive andthe like, it is important to keep the linearity between the displacementamount of the movable sections 20 a and 20 b and the driving voltage oroutput voltage. For this reason, it is preferable to use a materialhaving a small strain history, as well as having a coercive electricfield of 10 kV/mm or smaller.

Specific examples of the piezo-electric/electrostrictive layer 22 areceramics containing lead zirconate, lead titanate, magnesium leadniobate, nickel lead niobate, zinc lead niobate, manganese lead niobate,antimony lead stannate, manganese lead tungstate, cobalt lead niobate,barium titanate, sodium tinanate bismuth, potassium-sodium niobate,srontium tantalate bismuth, and the like alone or in combinationthereof.

Among them, ceramics containing lead zirconate, lead titanate, andmagnesium lead niobate as a main component, and ceramics containingsodium titanate bismuth as a main component are preferred. This isbecause these ceramics have high electromechanical coupling factor andpiezoelectric constant, and exhibit small reactivity with the thin-platesections (ceramics) 12 a and 12 b when calcined to formpiezo-electric/electrostrictive layer 22. In addition, the resultantpiezo-electric/electrostrictive layer 22 has stable composition.

It is also possible to use ceramics containing, on top of theabove-described components, oxides of lanthanum, calcium, strontium,molybdenum, tungsten, barium, niobium, zinc, nickel, manganese, cerium,cadmium, chromium, cobalt, antimony, iron, yttrium, tantalum, lithium,bismuth, tin and the like alone or in combination thereof.

For example, by adding lanthanum and strontium to lead zirconate, leadtitanate, and lead niobate which are main components of the zirconia,there are advantages in some cases that the coercive electric field andpiezo-electric characteristics become controllable.

It is preferable to avoid the use of material subject to vitrification,such as silica. This is because a material such as silica easily reactswith the material of piezo-electric/electrostrictive layer 22 during theheat treatment thereof. As a result of the reaction with the silica, thecomposition of the piezo-electric/electrostrictive layer 22 fluctuatesand the piezo-electric characteristics thereof are impaired.

The pair of electrodes 24 and 26 formed in thepiezo-electric/electrostrictive elements 18 a and 18 b are preferablyconstituted by a metal which is in a solid state at a room temperatureand has high conductivity. Examples of such metals include aluminum,titanium, chromium, iron, cobalt, nickel, copper, zinc, niobium,molybdenum, ruthenium, palladium, rhodium, silver, tin, tantalum,tungsten, iridium, platinum, gold, lead, and alloys thereof.Alternatively, it is also possible to use a cermet material in which thesame material or a different material from the material used for thepiezo-electric/electrostrictive layer 22 or the material used for thethin plate sections 12 a and 12 b is dispersed.

The material of the electrodes 24 and 26 formed in thepiezo-electric/electrostrictive elements 18 a and 18 b is decideddepending on the method for forming the piezo-electric/electrostrictivelayer 22. For example, when the electrode 24 is formed on the thin platesections 12 a and 12 b, and after that thepiezo-electric/electrostrictive layer 22 is formed on the electrode 24by sintering, a high-melting point metal such as platinum, palladium,platinum-palladium alloy, silver-palladium alloy the like is required.On the other hand, when the electrode 26 is formed on thepiezo-electric/electrostrictive layer 22 as the outermost layer afterthe piezo-electric/electrostrictive layer 22, it may be formed at lowtemperature, and therefore, may be mainly made of a low-melting pointmetal such as aluminum, gold, silver and the like as a main component.

The thickness of the electrodes 24 and 26 may be a considerably largefactor that deteriorates the displacement of thepiezo-electric/electrostrictive elements 18 a and 18 b. Therefore, as amaterial of the electrode formed after the formation of thepiezo-electric/electrostrictive layer 22 by sintering, it is preferableto use an organometallic paste which forms a fine and thin film aftersintering, such as gold resinated paste, platinum resinated paste, andsilver reginated paste.

The above embodiment shows the case where the movable sections 20 a and20 b integrally formed with the thin plate sections 12 a and 12 b attheir top ends have a thickness larger than the thickness Dd of the thinplate sections 12 a and 12 b. Alternatively, the movable sections 20 aand 20 b may have a thickness substantially same as the thickness Dd ofthe thin plate sections 12 a and 12 b. With this arrangement, when anarticle is mounted to the movable sections 20 a and 20 b, the articlehaving a size matching the distance between the thin plate sections 12 aand 12 b can be mounted in such a manner as to be interposed between themovable sections 20 a and 20 b. In this case, the adhesive region (forexample, the adhesive 38) used for mounting the article corresponds tothe movable sections 20 a and 20 b.

This structure further has the following advantages. Thepiezo-electric/electrostrictive device 10 can be preferably used invarious sensors, such as ultrasonic sensors, acceleration sensors,angular velocity sensors, impact sensors, mass sensors and the like. Byproperly adjusting the size of the article to be mounted in a spaceextending from the end surfaces 34 a and 34 b to the thin plate sections12 a and 12 b, the sensitivity of the sensor can be easily adjusted.

Next, the piezo-electric/electrostrictive device 10 according to second,third and fourth embodiments where the end surfaces 34 a and 34 b areformed, will be described referring to FIG. 4-FIG. 8. However, thepresent invention can be carried out with no problem even if no endsurfaces 34 a and 34 b are formed.

In the second embodiment, the piezo-electric/electrostrictive device 10a has substantially the same structure as of thepiezo-electric/electrostrictive device 10 described above, as shown inFIG. 4, except that the structures of the recess and the filler aredifferent on the following points.

The recesses 14 a and 14 b have a step-like structure, and the portioncloser to the thin plate section has a larger depth. In this structure,the concentrated stress generated at the boundary between the thin platesections, and the movable sections and the fixing portion, can bedispersed more effectively. The portion of the recess larger in widthgreatly serves to absorb the impact and disperse the concentrated stressefficiently.

Particularly, the electrode 26 located under the first layer is formedto substantially continue over the side surface of the thin platesections 12 a and 12 b, the movable sections 20 a and 20 b to the fixingsection 14. Then, a part of the electrode 26 is separated at the sidesurface of the fixing portion 14 to form a slit 70. The slit 70 isformed for the following purposes: 1) to prevent the actuator fromdriving at the bottom end portion 72 of thepiezo-electric/electrostrictive elements 18 a and 18 b (i.e., theportion from the bottom end portion of the slit 70 to the bottom end ofthe fixing section 14); 2) to suppress the generation of short circuitat the end of the terminal 28; and 3) to provide an electrode materialunder the piezo-electric/electrostrictive layer 22 at the bottom end ofthe piezo-electric/electrostrictive elements 18 a and 18 b. If it is notpreferable to form the slit 70, the slit 70 is not necessarily formedand may be omitted.

FIG. 5 shows the shape of the filler filled into the recess. In theembodiment shown in FIG. 5(a), the filler fills the recess abouthalfway, and the area near the opening is free from the filler. If therecess has a hollow portion in which no filler is provided is formed atits bottom, the effect of dispersing the stress is not adverselyaffected. In the embodiment shown in FIG. 5(b), the filler is providedin the recess beyond the opening thereof. This arrangement isadvantageous where the filler has weak adhesion, because the filler canbe attached inside the recess in a large area thereby increasing theadhesion of the entire filler. By forming the outer surface of thefiller into R-shape, the filler can be more firmly fixed into therecess, and never peels off at its end portion. FIG. 5(c) shows the casewhere the filler is made of different materials from each other for therespective layers which form the recess together. It is preferable todetermine the combination of the materials to attain the effect ofdispersing the stress by properly selecting the physical properties ofthe materials such as degree of elasticity and porosity, and attachmentto the constituent elements.

The piezo-electric/electrostrictive device 10 b according to the thirdembodiment has a structure in which the recess shown in FIG. 6 is formedinto the tapered shape constituted by infinite multiple steps, whereasthe device shown in FIG. 4 has the recess formed into the shape of twosteps in its depth direction. The concentrated stress generated at theboundary between the thin plate sections, and the movable sections andthe fixing section can be effectively dispersed. The portion of therecess being larger in width greatly serves to adsorb an impact, andallows the concentrated stress to disperse efficiently.

FIG. 7 shows the shape of the filler to be filled in the recess. In theembodiment shown in FIG. 7(a), the filler is filled about halfway intothe recess, and the area near the opening is free from the filler. Ifthe recess has a hollow portion in which no filler is provided at itsbottom, the effect of dispersing the stress is not adversely affected.Contrarily, in the embodiment shown in FIG. 7(b), the filler is providedin the recess beyond the opening thereof. This arrangement isadvantageous where the filler has weak adhesion, because the filler canbe attached inside the recess in a large area thereby increasing theadhesion of the entire filler. By forming the outer surface of thefiller into R-shape, the filler can be more firmly fixed into therecess, and never peels off at its end portion.

In the piezo-electric/electrostrictive device 10 c according to thefourth embodiment, as shown in FIG. 8, the filler having a substantiallyuniform thickness is provided in the recess between the thin platesection, and the movable section and the fixing section. Such a filleris preferably formed at the same time that the thin plate sections areintegrally formed with the movable section and the fixing section usingceramics as a material. The preferable material of the filler is amixture of ceramics and high-melting point metal or high-melting pointmetal.

Next, the method for producing the piezo-electric/electrostrictivedevice 10 will be described referring to FIGS. 9 to 12.

The piezo-electric/electrostrictive device 10 includes constituentelements preferably made of ceramics. Among the constituent elements,the substrate 16 (except for the piezo-electric/electrostrictiveelements 18 a and 18 b), the thin plate sections 12 a and 12 b, thefixing section 14, and the movable sections 20 a and 20 b are preferablyproduced by a ceramic green sheet laminating method. On the other hand,the piezo-electric/electrostrictive elements 18 a and 18 b, and theterminals 28 and 30 are preferably made by a film formation method suchas that employed for forming thin films and thick films.

In a ceramic green sheet laminating method capable of integrally formingthe members of the substrate 16 of the piezo-electric/electrostrictivedevice 10, there arises almost no change in the state of connectionsbetween the members with the elapse of time. Therefore, this method isadvantageous to attain high reliability at the connections between themembers and has high rigidity.

In addition, the production method described below is excellent inproductivity and formability. Therefore, thepiezo-electric/electrostrictive device 10 can be produced into apredetermined shape with high reproducibility in a short time.

Hereinafter, the first method for producing thepiezo-electric/electrostrictive device 10 according to the embodiment ofthe present invention will be described. Herein, definitions are made asfollows. A laminated body obtained by laminating ceramic green sheets ontop of each other is defined as a ceramic green sheet 58 (for example,see FIG. 10). The ceramic green laminated body 58 is sintered andintegrated into a one-piece unit, and the resultant body is defined as aceramic laminated body 60. From the ceramic laminated body 60,unnecessary portions are cut off and removed, and the resultant body,including the movable sections 20 a and 20 b, thin plate sections 12 aand 12 b, and the fixing section 14 as an integrated one-piece unit isdefined as a ceramic substrate 16 (see FIG. 12).

In this production method, a plurality ofpiezo-electric/electrostrictive devices 10 are arranged on the samesubstrate in its longitudinal and lateral directions. Finally, theceramic laminated bodies 60 are cut off by the unit of chip to obtain aplurality of piezo-electric/electrostrictive devices 10 simultaneouslyin one step. However, in order to simplify the description, theproduction of only one piezo-electric/electrostrictive device 10 isshown.

First, a binder, a solvent, a dispersant, a plasticizer and the like areadded into a ceramic powder, such as zirconia, and mixed to prepare aslurry. The slurry is subjected to degassing, and after that, formedinto a ceramic green sheet by a method such as reverse coating or doctorblade.

The ceramic green sheet is processed into various shapes and thicknessesas shown in FIG. 9 by a method such as blanking using a mold and laserprocessing. As a result, a plurality of ceramic green sheets for formingsubstrates are obtained.

The details of the prepared ceramics green sheets 50A to 50D, 51A and51B, 52A and 52B are as follows. A plurality of (for example, four)ceramic green sheets 50A to 50D are formed with a window section 54 forforming the hole section at least between the thin plate sections 12 aand 12 b. A plurality of (for example, seven) ceramic green sheets 102Ato 102G are formed with a window section 54 for forming the hole sectionbetween the thin plate sections 12 a and 12 b, and a window section 100for forming the movable sections 20 a and 20 b with the end surfaces 34a and 34 b in an opposed relation to each other, and the window sections54 and 100 are joined into one window section. A plurality of (forexample, two) ceramic green sheets 51A and 51B are formed with a windowsection 100 a to be the recesses 14 a and 14 b. A plurality of (forexample, two) ceramic green sheets 52A and 52B to be the thin platesections 12 a and 12 b are formed.

After that, as shown in FIG. 10, the ceramic green sheets 50A to 50D,51A and 51B, and 102A to 102G are interposed between the ceramic greensheets 52A and 52B, and then, these ceramics green sheets 50A to 50D,51A, 51B, 52A and 52B, and 102A to 102G are laminated and crimped toform a ceramic green laminated body 58. In laminating these greensheets, the ceramic green sheets 102A to 102G are positioned at themiddle positions. Due to the presence of the window sections 100 and 100a, no pressure is applied to some sections of the green sheets in thestep of crimping. In order to prevent sections to which no pressure isapplied in the crimping from being created, it is necessary to alter thesequence of lamination and crimping. Then, the ceramic green laminatedbody 58 is sintered to obtain a ceramic laminated body 60 (see FIG. 11).

The number of times and the sequence of crimping for laminating andintegrating the green sheets into a one piece unit are not specificallylimited, and may be properly determined so that a ceramics laminatedbody in a desired structure can be obtained based on the structure ofthe ceramic green laminated body such as, for example, the shape of thewindow sections 54 and the number of ceramic green sheets.

It is not necessary that all the window sections 54 have the same shapeeach other, and their shapes may be determined in accordance with adesired function. In addition, the number of ceramic green sheets andthe thickness of each green sheet are not specifically limited.

By crimping the ceramic green sheets through the application of heat,they can be more firmly laminated. The lamination at the interfacesbetween the ceramic green sheets can be enhanced by applying ceramicspowder (it is preferable that this ceramics powder has a compositionsame or similar to the ceramics used as a material of the ceramic greensheets in order to attain high reliability), a paste containing a binderas a main component, slurry and the like. When the ceramic green sheets52A and 52B are thin, it is preferable to handle them using a plasticfilm, especially a polyethylene terephthalate film on which asilicone-based releasing agent is applied.

Next, as shown in FIG. 11, piezo-electric/electrostrictive elements 18 aand 18 b are formed on both surfaces of the ceramic laminated body 60,that is, on the surfaces corresponding to the surfaces on which theceramic green sheets 52A and 52B are laminated. As a method for formingthe piezo-electric/electrostrictive elements 18 a and 18 b, thick filmformation methods such as screen printing, dipping, coating, andelectrophoresis, and thin film forming methods such as ion beam,sputtering, vacuum deposition, ion plating, chemical vapor deposit(CVD), and plating may be employed.

By employing the film formation method as described above, thepiezo-electric/electrostrictive elements 18 a and 18 b are integrallyformed with the thin plate sections 12 a and 12 b without using anadhesive. As a result, high reliability and high reproducibility areattained, and the piezo-electric/electrostrictive elements 18 a and 18 bcan easily be integrally formed with the thin plate sections 12 a and 12b.

In this case, it is preferable to employ the thick film formation methodfor forming the piezo-electric/electrostrictive elements 18 a and 18 b.The thick film formation method is especially advantageous in formingthe piezo-electric/electrostrictive layer 22. In this case, a greensheet can be formed using a paste, slurry, suspension, or emulsioncontaining piezo-electric ceramic particles and powder having an averageparticle diameter of 0.01 to 5 μm, and preferably 0.05 to 3 μm. Bysintering the green sheet, a layer with excellentpiezo-electric/electrostrictive characteristics can be obtained.

The electrophoresis is advantageous in that it forms a layer with highdensity and high shape precision. Screen printing provides simultaneousfilm formation and pattern formation, and is therefore advantageous insimplifying production.

The formation of the piezo-electric/electrostrictive elements 18 a and18 b will be specifically described. First, the ceramic green laminatedbody 58 is sintered and integrated at a temperature of 1200 to 1600° C.to obtain the ceramic laminated body 60. Next, the first electrode 24 ofthe thin plate sections 12 a and 12 b is printed at a predeterminedposition on both surfaces of the ceramic laminated body 60, and then issintered. Then, the piezo-electric/electrostrictive layer 22 is printedand is sintered. After that, the other electrode 26 which pairs up withthe electrode 24, is printed and sintered. These steps are repeated apredetermined number of times (if the piezo-electric/electrostrictiveelements 18 a and 18 b are constituted by a multilayeredpiezo-electric/electrostrictive layer 22), and as a result, thepiezo-electric/electrostrictive elements 18 a and 18 b are formed. Afterthat, terminals 28 and 30 for electrically connecting the electrodes 24and 26 to the driving circuit are printed and sintered.

Alternatively, the first electrodes 24 in the bottom layer are printedand sintered. Then, the piezo-electric/electrostrictive layer 22, andthe other electrode 26 which pairs up with the electrode 24 is printedand sintered. The printing and sintering steps are repeated in thisorder in predetermined number of times to obtain thepiezo-electric/electrostrictive elements 18 a and 18 b.

By selecting the materials of members in such a manner that thesintering temperatures become gradually lower in accordance with theorder of lamination, for example, platinum (Pt) for the electrode 24,lead zirconate titanate (PZT) for the piezo-electric/electrostrictivelayer 22, gold (Au) for the electrode 26, and silver (Ag) for theterminals 28 and 30, the material which has been already sintered is notsintered again at a certain sintering stage. In this manner, troublessuch as peeling and coagulation of the electrode materials and the likecan be avoided.

It is also possible to sequentially print the members of thepiezo-electric/electrostrictive elements 18 a and 18 b and the terminals28 and 30, and to sinter and integrate them at a time by selectingproper materials. In addition, after forming thepiezo-electric/electrostrictive layer 22, which is the outermost layer,the electrode 26 on the outermost layer can be formed at a lowtemperature.

The members of the piezo-electric/electrostrictive elements 18 a and 18b, and the terminals 28 and 30, may be formed by a thin film formationmethod such as sputtering and deposition. In this case, heat treatmentis not necessarily conducted.

In the formation of the piezo-electric/electrostrictive elements 18 aand 18 b, it is also preferred that the piezo-electric/electrostrictiveelements 18 a and 18 b are formed beforehand on both surfaces of theceramic green laminated body 58, that is, on the surfaces of the ceramicgreen sheets 52A and 52B, and the ceramic green laminated body 58 andthe piezo-electric/electrostrictive elements 18 a and 18 b aresimultaneously sintered. As to the simultaneous sintering, all the filmsconstituting the ceramic green laminated body 58 and thepiezo-electric/electrostrictive elements 18 a and 18 b may be sintered.It is also possible to simultaneously sinter the electrodes 24 and theceramic green laminated body 58, or to simultaneously sinter all thefilm constituting the members except for the electrode 26 and theceramic green laminated body 58.

The piezo-electric/electrostrictive elements 18 a and 18 b and theceramic green laminate body 58 may be simultaneously sintered by thefollowing steps. First, a precursor of thepiezo-electric/electrostrictive layer 22 is formed by a tape formingmethod using a slurry raw material. The precursor of thepiezo-electric/electrostrictive layer 22 before sintering is laminatedon the surface of the ceramic green laminated body 58 by a method suchas heat deposition, and at the same time, is sintered to simultaneouslyform the movable sections 20 a and 20 b, the thin plate sections 12 aand 12 b, the piezo-electric/electrostrictive layer 22, and the fixingsection 14. In this method, however, it is necessary to form theelectrode 24 on the surface of the ceramic green laminated body 58and/or the piezo-electric/electrostrictive layer 22 beforehand.

Alternatively, different steps from the above may be employed forsimultaneously sintering the piezo-electric/electrostrictive elements 18a and 18 b and the ceramic green laminate body 58. That is, theelectrodes 24 and 26, and piezo-electric/electrostrictive layer 22,which are constituent elements of the piezo-electric/electrostrictiveelements 18 a and 18 b, are formed on the ceramic green laminated body58 at the positions which are finally the thin plate sections 12 a and12 b, and are sintered simultaneously.

The temperature employed for sintering the constituent elements of thepiezo-electric/electrostrictive elements 18 a and 18 b is determined inaccordance with the material of the constituent elements. In general,the temperature is 500 to 1500° C., and as to thepiezo-electric/electrostrictive layer 22, preferably 1000 to 1400° C. Inthis case, in order to control the composition of thepiezo-electric/electrostrictive layer 22, the material thereof ispreferably calcined in the presence of the evaporation source. When thepiezo-electric/electrostrictive layer 22 and the ceramic green laminatedbody 58 are sintered simultaneously, it is necessary to sinter themunder the same conditions. The piezo-electric/electrostrictive elements18 a and 18 b are not necessarily formed on both surfaces of the ceramiclaminated body 60 or the ceramic green laminated body 58, and may beformed only one of the surfaces thereof.

Next, the ceramic laminated body 60 on which thepiezo-electric/electrostrictive elements 18 a and 18 b are formed is cutalong the cutting lines C1, C2, and C5 to remove the side portions andthe top ends of the ceramic laminated body 60. By cutting the ceramiclaminated body 60, as shown in FIG. 12, thepiezo-electric/electrostrictive device 10 is obtained where the ceramicsubstrate 16 includes the piezo-electric/electrostrictive elements 18 aand 18 b, and movable sections 20 a and 20 b having the end surfaces 34a and 34 b in an opposed relation to each other. The ceramic laminatedbody 60 may be cut along the line C1 and C2 first, and then, along theline C5, or may be cut along the cutting line C5, and then, along thelines C1 and C2. It is also possible that the ceramic laminated body 60may be cut along the cutting lines C1, C2, and C5 simultaneously. Theend surface of the fixing section 14 in an opposed relation to thecutting line C5 may be properly cut when, for example, the entire lengthof the piezo-electric/electrostrictive device is precisely controlled.

In the production method described above, unnecessary portions are cutand removed from the ceramic laminated body 60. The obtainedpiezo-electric/electrostrictive device 10 includes thepiezo-electric/electrostrictive elements 18 a and 18 b on the ceramicsubstrate 16, and the movable sections 20 a and 20 b having the endsurfaces 34 a and 34 b. In this method, the production steps can besimplified, and the yield of the piezo-electric/electrostrictive device10 can be increased. It is especially preferable that a plurality ofpiezo-electric/electrostrictive devices 10 are arranged on the samesubstrate in its longitudinal and lateral directions respectively toobtain a plurality of devices in one step.

The ceramic laminated body may be cut by mechanical processings such asdicing and wire saw processing, laser processing with YAG laser, excimerlaser, electron beam and the like.

When the ceramic substrate 16 is cut, the above-described processingsare employed in combination. It is preferable, for example, wire sawprocessing is employed for cutting along the lines C1 and C2 (see FIG.11), and dicing is employed for cutting the fixing sections 14perpendicular to the cutting lines C1 and C2, and the end surface ofmovable sections 20 a and 20 b.

In the above-described method for producing thepiezo-electric/electrostrictive device 10, thepiezo-electric/electrostrictive elements 18 a and 18 b are formed on thethin plate sections 12 a and 12 b by sintering and integrating them intoa one-piece unit. The thin plate sections 12 a and 12 b, and thepiezo-electric/electrostrictive elements 18 a and 18 b are slightlydisplaced to project toward the hole section 42, and become deformed dueto the shrinkage of the piezo-electric/electrostrictive layer 22, andthe difference in thermal coefficients between the pair of electrodes 24and 26 and the thin plate sections 12 a and 12 b. As a result, internalresidue stress tends to be generated in thepiezo-electric/electrostrictive elements 18 a and 18 b (and especiallypiezo-electric/electrostrictive layer 22) and the thin plate sections 12a and 12 b.

The internal residue stress is also generated in the thin plate sections12 a and 12 b, and the piezo-electric/electrostrictive layer 22 when thepiezo-electric/electrostrictive elements 18 a and 18 b are attached tothe thin plate sections 12 a and 12 b as separated members, besides inthe integration by sintering described above. That is, when the adhesiveis stabilized or cured, the adhesive shrinks on curing to cause theinternal residue stress to generate in the thin plate sections 12 a and12 b, and the piezo-electric/electrostrictive layer 22. Furthermore, ifthe adhesive requires heat application at the time of stabilization orcuring, larger internal residue stress is generated.

If the piezo-electric/electrostrictive device 10 is used in this state,there are cases where the movable sections 20 a and 20 b do not exhibita desired amount of displacement even if a specified electric field isapplied to the piezo-electric/electrostrictive layer 22. This is becausethe internal residue stress generated in the thin plate sections 12 aand 12 b, and the piezo-electric/electrostrictive layer 22 damages thematerial characteristics of the piezo-electric/electrostrictive layer22, and impedes the displacement movement of the movable sections 20 aand 20 b.

In order to avoid such trouble, in the production method of the presentinvention, the peripheral portions of the movable sections 20 a and 20 bare cut and removed after the piezo-electric/electrostrictive elements18 a and 18 b are formed. As a result of cutting, the end surfaces 34 aand 34 b in an opposed relation to each other are formed on the movablesections 20 a and 20 b respectively. The end surfaces 34 a and 34 bmoves in a direction that they get close to each other by the internalresidue stress generated in the thin plate sections 12 a and 12 b, andthe piezo-electric/electrostrictive layer 22. The width between the endsurfaces 34 a and 34 b after they get close to each other becomes asecond specified width W2 which is shorter than the specified width W1.More specifically, the second specified width W2 does not extendstraightly, but gradually decreases in an upward direction and issmaller at the top ends of the end surfaces 34 a and 34 b than thebottom ends thereof.

The end surfaces 34 a and 34 b move when the internal residue stress isgenerated in the thin plate sections 12 a and 12 b, and thepiezo-electric/electrostrictive layer 22 is released. If thepiezo-electric/electrostrictive device 10 is used in the state where theinternal residue stress is released, the movable sections 20 a and 20 bexhibit the displacement movement substantially as designed, and as aresult, the device 10 exhibits excellent characteristics. The sameeffect can be obtained in the case where the end surfaces 34 a and 34 bin an opposed relation to each other are formed in the fixing section 14by cutting a part of the portion to be the fixing section 14. In thiscase, the internal stress generated in the thin plate sections 12 a and12 b, and the piezo-electric/electrostrictive layer 22 is released bythe movement of the end surfaces 34 a and 34 b in an opposed relation toeach other formed in the fixing section 14. The end surfaces 34 a and 34b are not necessarily formed at a middle area of the movable sections 20a and 20 b or the fixing section 14, and the same effect can be obtainedwhen they are formed at positions depart from the middle area.

In the cutting step shown in FIG. 11, the ceramic laminated body afterbeing cut is preferably heated at 300 to 800° C. for the followingreason. As a result of the cutting process, defects, such as microcracks, tend to be created in the piezo-electric/electrostrictive device10. These defects can be reduced by being heated, and high reliabilitycan be attained. After the heat treatment, the ceramic laminated body issubjected to an aging treatment where it is held at about 80° C. for atleast 10 hours. In the aging treatment, various stresses received in theproduction steps can be further decreased thereby increasing thecharacteristics of the device.

As described above, according to the present invention, a recess filledwith a filler is present between at least the thin plate section andmovable section, or between the thin plate section and the fixingsection. With this arrangement, even if the thin plate sections createlarge displacement by receiving a large impact from the outside, andstress is generated at a boundary between the thin plate section and themovable section or between the thin plate section and the fixingsection, the stress is dispersed into the filler provided in the recess.In this manner, there is no damage which has conventionally resultedfrom the concentration of stress, and there is only a small influence tothe basic properties of the piezo-electric/electrostrictive device. As aresult, the impact resistance of the thin plate sections is enhanced.

1. A piezoelectric/electrostrictive device comprising: a pair of thinplate sections in an opposed relation to each other, a movable sectionat a top end of each of the thin plate sections; a fixing section forsupporting the thin plate sections; and at least onepiezoelectric/electrostrictive element coupled to at least one of thethin plate sections; wherein portions of the thin plate sections arespaced from portions of the movable section to form recessestherebetween.
 2. A piezoelectric/electrostrictive device according toclaim 1, wherein portions of the thin plate sections are also spacedfrom portions of the fixing section to form recesses therebetween.
 3. Apiezoelectric/electrostrictive device comprising: a pair of thin platesections in an opposed relation to each other; a movable section at atop end of each of the thin plate sections; a fixing section forsupporting the thin plate sections; and at least onepiezoelectric/electrostrictive element coupled to at least one of thethin plate sections; wherein portions of the thin plate sections arespaced from portions of the fixing section to form recessestherebetween.
 4. A piezoelectric/electrostrictive device comprising: apair of thin plate sections in an opposed relation to each other; amovable section at a top end of each of said thin plate sections; afixing section for supporting said thin plate sections; and at least onepiezoelectric/electrostrictive element coupled to at least one of saidthin plate sections; wherein portions of said thin plate sections arespaced apart from portions of at least one of said movable section andsaid fixing section to form recesses therebetween.
 5. Thepiezoelectric/electrostrictive device of claim 4, further comprising afiller material provided in at least a portion of said recesses.
 6. Thepiezoelectric/electrostrictive device of claim 5, wherein said filler isprovided such that a portion of each said recess proximate an openingthereof is free of said filler.
 7. The piezoelectric/electrostrictivedevice of claim 5, wherein said filler comprises a protruding portionthat protrudes a distance beyond an opening of said recesses, saidprotruding portion defining a sloped contour surface between a surfaceof at least one of said moveable section and said fixing section and aninner surface of said thin plate section.
 8. Thepiezoelectric/electrostrictive device of claim 5, wherein said fillercomprises a protruding portion that protrudes a distance beyond anopening of said recesses, said protruding portion defining at least onestep between a surface of at least one of said moveable section and saidfixing section and an inner surface of said thin plate section.
 9. Thepiezoelectric/electrostrictive device of claim 4, wherein said recessescomprise two or more step portions defined between an inner surface ofsaid thin plate section and a surface of at least one of said moveablesection and said fixing section.
 10. The piezoelectric/electrostrictivedevice of claim 5, wherein said filler has a substantially constantthickness within said recesses.
 11. The piezoelectric/electrostrictivedevice of claim 5, wherein said filler comprises a cermet.
 12. Thepiezoelectric/electrostrictive device of claim 4, wherein said recessescomprise a tapered surface defined between an inner surface of said thinplate section and a surface of at least one of said moveable section andsaid fixing section.
 13. The piezoelectric/electrostrictive device ofclaim 12, further comprising a filler material provided in at least aportion of said recesses.
 14. The piezoelectric/electrostrictive deviceof claim 13, wherein said filler is provided such that a portion of eachsaid recess proximate an opening thereof is free of said filler.
 15. Thepiezoelectric/electrostrictive device of claim 13, wherein said fillercomprises a protruding portion that protrudes a distance beyond anopening of said recesses, said protruding portion defining a slopedcontour surface between at least one surface of said at least one ofsaid moveable section and said fixing section and said inner surface ofsaid thin plate section.